1. Field of the Invention
The present invention relates to a radiation image detecting device for detecting a radiographic image of a sample, and a method for detecting the start of irradiation with radiation.
2. Description Related to the Prior Art
In a medical field, an X-ray imaging system using X-rays is known as a type of radiation imaging systems. The X-ray imaging system is constituted of an X-ray source for generating the X-rays, and an X-ray image detecting device that receives the X-rays having passed through a sample and detects an X-ray image of the sample. A type of the X-ray image detecting devices that has a flat panel detector (FPD) is in practical use. The FPD includes a TFT (thin film transistor) active matrix substrate having plural pixels arranged in two dimensions, and each pixel accumulates signal charge by an amount corresponding to the amount of the X-rays incident thereon. The FPD detects the X-ray image, which represents image information of the sample, by accumulating the signal charge on a pixel-by-pixel basis, and outputs the X-ray image as digital image data.
The X-ray image detecting device using the FPD, in contrast to the other types of X-ray image detecting devices using a film or an imaging plate (IP), needs to be synchronized with the X-ray source, such that the FPD accumulates the signal charge concurrently with emission of the X-rays from the X-ray source. Accordingly, a controller e.g. a console of the X-ray image detecting device synchronizes the start of charge accumulation operation by the FPD with the start of X-ray emission by the X-ray source, which is triggered by a push of an emission switch connected to the X-ray source. Specifically speaking, the controller receives an emission start signal issued from the emission switch, and outputs this signal as a synchronization signal to the X-ray image detecting device. Upon receiving the synchronization signal, the X-ray image detecting device shifts to the charge accumulation operation, and starts capturing the X-ray image.
However, when the X-ray image detecting device and the X-ray source are manufactured by different makers, the X-ray image detecting device and its controller are sometimes outfitted with a synchronization control interface incompatible with that of the X-ray source (as to specifications of a cable and a connector, the format of the synchronization signal, and the like). Therefore, various self-detection techniques are proposed in which the X-ray image detecting device detects the start of X-ray irradiation by itself without using the synchronization signal, for synchronization with the X-ray source (refer to U.S. Pat. No. 6,801,598 corresponding to Japanese Patent Laid-Open Publication No. 2003-126072, U.S. Pat. No. 6,797,960 corresponding to Japanese Unexamined Patent Application Publication No. 2002-543684, and U.S. Pat. No. 8,045,680 corresponding to Japanese Patent Laid-Open Publication No. 2008-125903).
According to the self-detection techniques disclosed in the above patent documents, however, when noise (hereinafter called shock noise) caused by shock, vibration or the like occurs, the X-ray image detecting device could wrongly detect the shock noise as the start of X-ray irradiation, and shift to the charge accumulation operation. In spite of this fact, the above patent documents do not describe or even suggest an object of preventing the misdetection caused by the shock noise and measures against it.